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Sun C.-Q.,China Earthquake Administration | Yan C.-H.,Earthquake Bureau of the Guangxi Zhuang Autonomous Region | Wu X.-P.,Yunnan University | Xu Y.-J.,Earthquake Bureau of Yunnan Province
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2014

In this study, according to the Harvard CMT catalog, the tidal normal stress, shear stress, Coulomb failure stress and phase angle on the surface of seismic fault of 363 earthquakes were calculated in eastern Tibetan plateau and its neighboring areas, which were divided into 5 tectonic districts. Tidal stress components on different kinds of seismogenic fault and its variation characteristics with depth were analyzed. Using Coulomb failure stress criterion, the effect of tidal triggering on various earthquakes was obtained. The Schuster's test was used to analyze the effect of tidal stress on earthquakes of different magnitude and tectonic types. Using the two methods above mentioned comprehensively, we explored the effect of tidal triggering on earthquakes of different magnitude, tectonic district, seismogenic fault and depth. Our results show that tidal triggering was obvious on normal and thrust fault earthquakes in Indian block and Lhasa block, strike and oblique slip fault earthquakes in Yunnan-Myanmar-Thailand block, Indochina block and Songpan-Garzê block, oblique slip fault earthquakes in Sichuan-Yunnan Diamond block. Moreover, the effect of tidal triggering depended on the depth and magnitude of earthquake, the fault of seismogenic fault and regional tectonic stress field. Source


Yan C.-H.,Earthquake Bureau of the Guangxi Zhuang Autonomous Region | Zhou B.,Earthquake Bureau of the Guangxi Zhuang Autonomous Region | Zhou B.,China Earthquake Administration | Lu L.-J.,Earthquake Bureau of the Guangxi Zhuang Autonomous Region | And 2 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2015

Based on the precise relocation results of 3682 earthquakes occurred in the Longtan reservoir from September 30, 2006 to May 26, 2013, focal mechanisms of events with magnitude greater than or equal to ML2.0 and regional tectonic stress field have been inverted using the FOCMEC method and modified grid search method. Considering stratum lithology, fault and penetrative conditions, the relationship between seismic mechanism types and reservoir storage processing were discussed, and the following conclusions could be reached: (1) Earthquakes after the Longtan reservoir recharged were mainly clustered in the 5 deep water level regions which are Luotuo, Bamao, Lalang, Bashou and Buliuhe. The main types of focal mechanism solutions are thrust faults, and normal and strike-slip faults are also present in a certain proportion. Focal mechanism types are multiplex in the early water storage stage of the Longtan reservoir. About 4 years and 3 months later, earthquakes mainly occurred in the shallow subsurface, where exist most thrust faults. (2) Dominant direction of the maximum principal stress of regional tectonic stress field in 5 earthquake clusters is in NW-SE, and its dip angle is very small. The parameter distributions of the middle and the minimum principal stress are irregular. In such an in-situ stress environment, most of the main fractures in the Longtan reservoir area exhibits a nature of strike-slip movement, and a few of them accompanied with thrust or normal movement components to some extent. (3) The depth of hypocenter and focal mechanism of earthquake change with reservoir storage process, which may be related to the differences such as the tectonic stress environment, mechanical properties of rock mass and penetrability in the shallow and deep subsurface. © 2015, Science Press. All right reserved. Source


Zhou B.,Earthquake Bureau of the Guangxi Zhuang Autonomous Region | Zhou B.,China Earthquake Administration | Sun F.,China University of Petroleum - East China | Yan C.-H.,Earthquake Bureau of the Guangxi Zhuang Autonomous Region | And 2 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2014

In order to know the dynamic response mechanism of reservoir-induced seismicity (RIS), this paper has established the quantitative mathematical model and taken the Longtan reservoir as an example, established a 3D-poreelastic finite element model according to geologic structure, deep velocity structure and digital elevation of the reservoir area, calculated the dynamic changes of pore pressure, effective additional normal stress, shear stress and Coulomb failure stress in the faults and rocks at bottom of the reservoir during the process of reservoir storage impounding. Combined with the characteristics of seismic activity in the temporal and spatial distribution of the reservoir area after impoundment, the relationship between the evolution of RIS in space-time and the process of reservoir water body load-unloading and water infiltration, and their possible mechanism have been discussed. Our study shows that: (1) After impoundment of the reservoir in September 30, 2006, seismic activity level around the Longtan reservoir obviously enhanced, and earthquakes mainly concentrated in 5 flooded deepwater areas, that are Luotuo (Cluster I), Bamao (Cluster II), Lalang (Cluster III), Dam head (Cluster IV) and Buliu River (Cluster V) earthquake clusters. The above areas were also the most obviously increasing areas of ΔCFS during the process of reservoir water body load-unloading and water infiltration, but there were seldom earthquakes in the shadow area of ΔCFS. It indicates that there exists closely relationship between variation of ΔCFS and reservoir seismic activities after the impoundment of the Longtan reservoir. (2) Numerical simulation results show that those faults, which have better permeability and directly hydraulic connection with the reservoir, are the superior channels for additional water head pressure diffusion, through those channels, the affection of additional head pressure diffusion can almost reaches deep into 13 km under the ground, and those strata dominated by carbonate from Sinian to Paleozoic become main layer to receive the head pressure. The above results are consistent with the characteristics that focal depths around the Longtan reservoir have been totally less than 13 km and dominantly distributed in 5~10 km since impoundment. It indicates that pore pressure reduces the shear strength of rocks and partially offsets the effect of confining pressure, so rock mass at those layer are prone to induce seismicity. (3) Whether it is deep or shallow, there exists the vast majority of time overlaps between the intervals of earthquake occrence frequently and the intervals of ΔCFS rising acceleratedly or in high value stage. This maybe indicate that, being influenced by the rapid increase of external loading rate, rocks and faults at the bottom of the reservoir are more prone to become unstable. Meanwhile, the difference of seismic responding time, frequency and magnitude between the deep and the shallow may be related to inhomogeneity of mechanical properties and permeability in different strata. (4) There exists different physical and mechanical mechanism of RIS in the Longtan reservoir: Cluster I, II, III maybe have something to do with the effect of reservoir body gravity loading, pore pressure diffusing and water infiltration weakening; Cluster IV are mainly controlled by the action of reservoir body gravity loading, and the pore pressure diffusion and water infiltration weakening action does not play a leading role; Cluster V is mainly affected by the pore pressure diffusion and water infiltration weakening effect, the body gravity loading effect maybe hold down the seismicity in a certain extent. Source


Wen X.,Earthquake Bureau of the Guangxi Zhuang Autonomous Region | Miao C.,Earthquake Bureau of the Guangxi Zhuang Autonomous Region | Lu L.,Earthquake Bureau of the Guangxi Zhuang Autonomous Region | Zhang H.,Earthquake Bureau of the Guangxi Zhuang Autonomous Region | And 2 more authors.
Communications in Computer and Information Science | Year: 2015

To obtain the damaged building information rapidly and accurately can provide support for the disaster-relief work after the earthquake, and it is also an important part of the evaluation of the earthquake disaster losses. The high-resolution remote sensing image and the satellite radar data are important technical means for the disaster monitoring, but the accuracy of the automatic extraction of information is subject to certain restrictions. However in recent years, the newly-presented LiDAR technology can provide the elevation information for ground targets, which can be applied to rapidly and accurately extract the earthquake disaster information under the circumstances that the remote-sensing image is absent before the earthquake. Adopting the LiDAR data and remote sensing data in the Yushu disaster area, the damaged building information after the earthquake is automatically extracted through the Arcmap collection category samples and by using the object-oriented SVM classification, the overall accuracy can reach 80.96% in the research. © Springer-Verlag Berlin Heidelberg 2015. Source


Wen X.,Earthquake Bureau of the Guangxi Zhuang Autonomous Region | Zhang H.,Earthquake Bureau of the Guangxi Zhuang Autonomous Region | Zhou B.,Earthquake Bureau of the Guangxi Zhuang Autonomous Region | Huang H.,Earthquake Bureau of the Guangxi Zhuang Autonomous Region | Yuan Y.,Earthquake Bureau of the Guangxi Zhuang Autonomous Region
Communications in Computer and Information Science | Year: 2016

Continuous MODIS/Terra satellite remote sensing thermal infrared data of the 6.5-magnitude earthquake region in Ludian, Yunnan, from June to August 2014 were collected. Through cloud removing and other data treatments, the infrared data obtained during the optimal observation period from 5:00 a.m. to 7:00 a.m. of Beijing time were chosen for surface temperature retrieval. The relationship between the time-based evolution of anomalous surface temperature and anomalous space distribution, and the active fault before and after the earthquake was analyzed; the time and space relevance between the anomalous surface temperature and the latent heat flux changes was studied; and the influence of non-structural factors, such as landform and seasonal climate, on the anomalous surface is studied. Results suggested that: (1) one month before the occurrence of Ludian Earthquake, the epicenter showed anomalously increasing temperature of the thermal infrared, meaning that the anomalous temperature increase was related to the earthquake occurrence time; the significant temperature increase lasted for half a month before the earthquake, and the anomalous temperature increase reached the peak five to six days before the earthquake, but it decreased dramatically after the earthquake; (2) based on the hyperspectral data and the geological observation meteorological data, the influence of clouds and vegetation cover in the earthquake area was removed. The latent heat flux changes inverted showed a close time and space relevance with the anomalous surface temperature increase; (3) the analysis of the relevance with the landform and the seasonal climate factors suggested that there was structural “temperature increase” information of out-of-season changes before the earthquake; (4) the anomalous temperature increase developed in the shape of “X” from the epicenter to the conjugate fault. This coincided with the mechanical effect generated by the “L-shaped” asymmetric conjugated fault extended in the NW-SE direction of the advantageous distribution of the horizontal maximum principal stress and the NW~EW direction after the earthquake. Considering the influence of landform, seasonal climate and other non-structural factors on anomalous temperature increase, the author thought that the temperature increase of the thermal infrared might be a short-term anomalous phenomenon before the earthquake. © Springer-Verlag Berlin Heidelberg 2016. Source

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